Plan to replace some parking spaces on Polk Street with bicycle lanes and parklets has many residents and lots of business owners saying 'Not so fast.'

A cyclist rides up Polk Street in San Francisco past people sitting in a parklet… (Katie Falkenberg, Los Angeles…)

SAN FRANCISCO — Russian Hill's Velvet Da Vinci gallery, which offers an array of edgy jewelry and metalwork, has been doing brisk business lately in "Save Polk St." T-shirts.

Neighboring shops have signs in their display windows warning that a "radical agenda" threatens the shopping district, where residents can get shoes fixed at Frank's, fill pantries at Real Food Co., sip a Soju cocktail at Amelie or buy a silicone sex toy at Good Vibrations.

Just what is jeopardizing the vital north-south corridor — which provides a flat route, by San Francisco standards — from the Civic Center to the bay?

An ambitious street redesign that many residents and business owners say could strip the majority of curbside parking spots from a 20-block commercial stretch, replacing them with bike lanes and miniature parks.

To urban planners and bicycle enthusiasts, Polk Street is a key to San Francisco's 4-decade-old "transit-first" policy, designed to reduce the reliance on private cars in the second-most-densely populated city in the U.S.

But to the more than 300 vocal denizens of Polk Gulch, who packed a standing-room-only neighborhood meeting last week, the proposal is a commerce killer, one that would create "a freeway for bikes," with little benefit to shops along the route.

"The agenda is that they really want to get rid of cars," Velvet Da Vinci co-owner Mike Holmes said. "There's no better way of doing that than making sure there [is] no place to park.… This is social engineering on a really crazy scale."

Officials seemed taken aback by the anger at the Middle Polk Neighborhood Assn. gathering. Every seat in the Old First Presbyterian Church's community room was filled. The crowd stood several deep along the walls and spilled out into the corridor.

Audience members jeered when Edward D. Reiskin, the city's transportation director, couldn't say how many of the 320 curbside parking spots along Polk could be taken out under the plan.

"I don't have that data," he said to loud boos, before going with "something like 170" maximum. The response from the crowd was more of the same.

Only a few of the San Francisco Bicycle Coalition's 12,000 members seemed to be in attendance, and they remained largely silent — "intimidated" was how several attendees described it. The bike proponents who did speak were met with disdain.

Adrienne Schroeder, a 36-year-old neighborhood resident, argued that a cycling thoroughfare was a kind of Darwinian opportunity for the century-old commercial district. To the merchants who might be forced to close their doors, she said, "We'll fill your spot if you don't survive. This is an opportunity to create more businesses."

Transportation politics have never been smooth in San Francisco, a graceful, hilly city where activism is a contact sport. A populist "freeway revolt" more than half a century ago kept the broad thoroughfares to a minimum here.

So although bicyclists decry what they say are unsafe, poorly maintained streets, many motorists say they too feel under attack. They cite the city's efforts to roll out new parking meters and the axing of free curbside parking Sundays. And they complain bitterly about what they view as bad cycling behavior.

Chris Bucchere has become Exhibit A in the argument. On Thursday, the 36-year-old cyclist and software engineer pleaded not guilty to felony vehicular manslaughter for striking and killing an elderly pedestrian in a crosswalk last year.

But amid all the disagreement, the transit-first policy is clear: "Within San Francisco, travel by public transit, by bicycle and on foot must be an attractive alternative to travel by private automobile."

To that end, 25 miles of bike paths have been created in the last three years. And officials have passed ambitious transit goals. Fifty percent of all travel within the city's 49 square miles should be by something other than private vehicles by 2018, and 20% should be via bike by 2020.

Leah Shahum, executive director of the bike coalition, noted that certain neighborhoods are well on the way. In the Mission District, she said, 15% of all commutes are by bicycle.

"Even with relatively meager investments in bicycle infrastructure, we're seeing significant increases in the number of people biking," she said. "The city has already laid out its big-picture goals. [Polk Street] is a piece of the greater goal."

During last week's meeting, Reiskin told the restive audience that improved safety for cyclists and pedestrians was key to the redesign.

The street has one of the higher rates of collisions in the city, he said. "Once a month, a pedestrian or cyclist is getting hit by a car.… That's not good for anyone."

Polk needs repaving, and a 2011 bond measure has provided money to resurface the street and redesign it at the same time. Under consideration are separated bike paths, boarding islands for buses and expanded parklets to calm traffic, among other measures.